1. Field of the Invention
This invention relates to an exhaust gas-purifying system for internal combustion engines, which has unburnt gas component-adsorbing means arranged in the exhaust passage of the engine, for adsorbing unburnt gas components present in exhaust gases.
2. Prior Art
When an internal combustion engine is started, especially in a cold state, an exhaust gas-purifying catalyzer of the engine is not yet activated, so that unburnt gas components present in exhaust gases are unfavorably emitted into the air. To prevent emission of unburnt gases into the air, there has been proposed an exhaust gas-purifying system for internal combustion engines, by Japanese Provisional Utility Model Publication (Kokai) No. 4-105925, which includes unburnt gas component-adsorbing means arranged in the exhaust passage of the engine, for adsorbing unburnt gas components.
The above proposed exhaust gas-purifying system includes a bypass passage bypassing the unburnt gas component-adsorbing means, and a changeover valve for selectively guiding exhaust gases to the unburnt gas component-adsorbing means or through the bypass passage. The changeover valve is controlled such that before the temperature of the unburnt gas component-adsorbing means rises up to a predetermined value, exhaust gases are guided to the unburnt gas component-adsorbing means, whereby unburnt gas components in the exhaust gases are adsorbed by the exhaust gas component-adsorbing means, whereas after the temperature of the unburnt gas component-adsorbing means has reached the predetermined value, exhaust gases are guided through the bypass passage, to thereby prevent the unburnt gas components from being purged from the unburnt gas component-adsorbing means.
However, since the proposed exhaust gas-purifying system thus determines the adsorbed state of unburnt gas components, based on the temperature of the unburnt gas component-adsorbing means, the accuracy of determination of the adsorbed state of unburnt gas components is not always sufficient. As a result, even when the unburnt gas component-adsorbing means still has capacity for adsorbing the unburnt gas components, the bypass passage is unfavorably opened, so that unburnt gas components are guided to pass through the exhaust gas-purifying catalyzer, which has not been activated yet, and then emitted into the air. On the other hand, even when the unburnt gas component-adsorbing means is fully charged with unburnt gas components and hence purging of unburnt gas components is started, the bypass passage is not opened, so that the purged unburnt gas components are emitted into the air.